Chlorophyll is the pigment that gives plants and algae their green color. Plants use chlorophyll to trap light needed for photosynthesis . The basic structure of chlorophyll is a porphyrin ring similar to that of heme in hemoglobin, although the central atom in chlorophyll is magnesium instead of iron. The long hydrocarbon (phytol) tail attached to the porphyrin ring makes chlorophyll fat-soluble and insoluble in water. Chlorophyll a and chlorophyll b represent about 99% of the chlorophyll species found in edible plants (Figure 1; , while some algae and microalgae contain minor quantities of chlorophyll c pigments (e.g., Laminaria ochroleuca, Undaria pinnatifida) . Chlorophyll a and b only have a small difference in one of the side chains but an intact phytol tail, while the common characteristic of chlorophyll c isoforms is the absence of a phytol tail. These structural differences cause each type of chlorophyll to absorb light at slightly different wavelengths.
Metallo-chlorophyll derivatives, including chlorophyllins, can be chemically synthesized or produced in industrial food processing; these compounds contain zinc, iron, or copper in place of the central magnesium atom . The most studied chlorophyllin, sodium copper chlorophyllin (SCC), is a semi-synthetic mixture of sodium copper salts derived from chlorophyll . SCC is often simply called ‘chlorophyllin’ in the older scientific literature, with newer publications specifying whether iron, zinc, copper, or magnesium chlorophyllin were studied. During its synthesis, the magnesium atom at the center of the ring is replaced with copper (or other metals), and the phytol tail is lost. Unlike natural chlorophyll, chlorophyllins (regardless of the metal used) are water-soluble. Although the content of different SCC mixtures may vary, two compounds commonly found in commercial SCC are trisodium copper chlorin e6 and disodium copper chlorin e4 .